Integrated power controlled solenoid



Dec. 5, 1967 Q c. D. BUSHNELL 3, 6, 0

INTEGRATED POWER CONTROLLED SOLENOID Filed Feb. 19, 1965 BY j %ufl United States Patent O 3,356,910 INTEGRATED POWER CONTROLLED SOLENOID Clayton D. Bushnell, Northridge, Calif., assignor to Whittaker Corporation, Los Angeles, Calif., a corporation of California Filed Feb. 19, 1965, Ser. No. 433,936 4 Claims. (Cl. 317-148.5)

ABSTRACT OF THE DISCLOSURE An electromagnet coil is connected in series with a resistor, a voltage source and a switch. The terminals of the resistance are connected respectively to the collector and emitter of a transistor. A transient voltage derived from the electromaguet when the switch is closed is applied between the base and emitter to lower the collector-emitter resistance value and thereby cause a large operating current to flow to the electromagnet to produce operation of an associated armature. The electromagnet is then in a magnetically saturated condition at which time the transient voltage disappears and the collector-emitter resistance value returns to its initial high value to thereby reduce the shunting effect on the resistance whereby electromagnet maintaining current for maintaining the armature in attracted position then flows at a low safe value.

The present invention relates to solenoids or electromagnets and in particular to energizing means and techniques useful in energizing the same.

The term solenoid or electromagnet is used herein in its broadest connotation and includes generally a coil for producing a magnetic flux and an element in the form of an armature or plunger movable in response to such flux in, for example, relays, actuators, valves and the like to produce either a direct result or a control operation.

It is well recognized that a relatively large current is required to flow in the coil in order to cause the armature or plunger to move from a normal unattracted position to its magnetically attracted position wherein then only a relatively small current is required to flow to maintain the armature or plunger in such attracted position. A distinction is thus made between these two currents of different magnitude, the former being referred to as the operating current and the latter current of smaller magnitude being referred to as the maintaining current.

It is desirable that the difference in magnitude of these two required currents be as small as possible to minimize the generation of heat in prolonged energization of the solenoid or electromagnet. Efforts in the past have been devoted to reduction of this difference or differential, and such efforts have usually resulted in an expensive or complicated structure. Another approach taken in the past to minimize this undesired generation of heat involved the use of auxiliary relay contacts which in effect are used to insert a current limiting resistance in series with the solenoid coil once the armature or plunger is in its attracted position.

In accordance with certain aspects of the present invention, a switching operation is performed without movable contacts and in accordance with the change in magnetic flux so as to produce the required large operating current and to automatically thereafter produce the smaller maintaining current.

It is therefore a general object of the present invention to provide an improved control for a solenoid, the control being integrated with magnetic flux conditions in the solenoid.

A specific object of the present invention is to provide a solenoid operated unit which responds quickly, has a low steady state power consumption, and is consistent in its operating time.

Another specific object of the present invention is to provide a solenoid operated unit of this character in which the response time is substantially unaffected by prior his tory involving, for example, a prolonged period of time during which the unit may have been inadvertently left in an on condition.

Another specific object of the present invention is to provide a solenoid operated unit of this character such that it meets the following conditions, namelyif the unit were inadvertently left on for a long period of time, there would be no excessive heating, and if switched off and on, it would still have the same initial response time as it had prior to such long period of on time.

Another specific object of the present invention is to provide a contactless system in which a switching function is controlled by the solenoid magnetic field.

Another object of the present invention is to provide a system of this character which is simple and comparatively inexpensive, and consistent with a high degree of reliability.

Another specific object of the present invention is to provide a system of this character in which switching is accomplished in a solid state contactless device and in accordance with the solenoid magnetic field.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. This invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, may be best understood by reference to the following description taken in connection with the accompanying drawings, in which:

The single figure of the drawings illustrates a system embodying features of the present invention.

Referring to the drawing, the solenoid or electromagnet is illustrated in its simplest form and, as illustrated, includes a coil 10, a stationary magnetic core 11 which is magnetized when the coil 10 is energized; and a movable armature or plunger 12 which, as illustrated, is in its nonattracted position against a stationary stop 13, the same being maintained on such stop 13 either by gravity or by a coil tension spring 15.

When the coil 10 is energized, the plunger or armature 12 moves through the air gap 16 between the end of the core 11 and the armature 12, and in the attracted position the armature 12 contacts the core 11.

In accordance with one aspect of the present invention, the coil 10 having the terminals 17 and 18 is wound on the core 11 together with an auxiliary coil 19, one terminal of the coil 19 being connected to the coil terminal 18 and the other terminal of coil 19 being connected to the base electrode 21 of transistor 22 having its emitter electr-ode 23 connected to coil terminal 18.

A resistor 25 is connected between the emitter electrode 23 and the collector electrode 24, such electrode 24 being connected to the positive terminal of a voltage source 28 having its negative terminal connectable through switch 30 to coil terminal 17.

The operation of the circuit is as follows with the switch 30 in its open position, as illustrated. The armature or plunger 12 is in its nonattracted position against stop 13 with an air gap 16 between the core 11 and armature 12. Upon closing of switch 30, a current begins to flow through a series circuit which includes: source 28, resistor 25, coil 10 and switch 30. This current because of the inductance of coil 10 on its core 11 increases at a particular rate. This change in current produces a change in magnetic flux in core 11, and such change in magnetic flux in turn induces a control voltage in winding or coil 19, such control voltage being'applied between the base and emitter electrodes of transistor 22 to cause the transistor 22 to become conductive, i.e. materially lessen the resistance between electrodes 24 and 23. Thus, the unit is in elfect divergently unstable, with the secondary winding 19 acting in a regenerative feedback system. As a result of the transistor 22 becoming conductive, the current through coil 10 continues to increase until the core 11 becomes magnetically saturated. When this saturated condition exists, there is substantially no further increase in magnetic flux in coil 11, and consequently, the voltage induced in coil 19 is lessened to the extent that the transistor 22 is automatically restored to its nonconductive condition; and this is so even though the switch 30 remains closed. At this stage of operations, the armature 12 is in its magnetically attracted condition and contacts the stationary core 11. The armature 12 is maintained in such attracted position by a limited amount of current flowing through coil 10, the current being limited in accordance with the magnitude of resistor 25.

During this steady statecondition wherein switch 30 remains closed, the core 11 is maintained in a magnetically saturated condition wherein a slightly lesser current in coil 10 would result in operation just out of saturation.

While the particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is so to cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. In a solenoid control in which a coil wound on a core produces a magnetic fiux to attract an armature when a switch is closed to connect the coil in a series circuit with a voltage source and a resistor, the improvement which resides in connecting the output terminals of a switching transistor across said resistor and controlling the on-oif condition of said transistor in accordance with changes in magnetic conditions in said core, said resistor being of sufficiently large magnitude to limit flow of current to said coil to a safe value during sustained closure of said switch.

2. In a solenoid control, a magnetizable core; a coil on said core; a resistor; a voltage source, a switch, a series circuit comprising said coil, source, resistor and switch; a transistor having a pair of output terminals and a pair of input terminals; said output terminals being connected in shunt with said resistor; an auxiliary coil on said core having its terminals connected to said input terminals, the

voltage induced in said auxiliary coil and applied to said transistor being effective to render said transistor conductive and effectively lower the resistance in said series circuit, said resistor being of sufiiciently large magnitude to limit flow of current to said coil to a safe value during sustained closure of said switch.

3. In asolenoid control, a coil; a-voltage source; impedance means; a switch; said coil, source, impedance means and switch being connected in a series circuit in which the intensity of the current flowing through the coil and the magnetic flux produced by such current are established essentially by said impedance means; and means responsive to change in said flux and producing a voltage in accordance with said change; and means responsive to said voltage and altering the magnitude of said impedance means, said impedance means being of sufliciently large magnitude to limit flow of current to said coil to a safe value during sustained closure of said switch.

4. In a solenoid control, a core; a coil on said core; a voltage source; impedance means; a switch; said coil, source, impedance means and switch being connected in a series circuit; an auxiliary coil on said core; a transistor having a pair of input terminals connected in series with said coil; said transistor having a pair of output terminals connected in shunt with said impedance means; said auxiliary coil applying a voltage to said input terminals upon a change in flux in said core to render said transistor conductive and thereby effectively lower the magnitude of said impedance means to, in turn, cause further change in said flux until the flux saturates said core after which there is substantially no voltage developed in said auxiliary coil and said transistor automatically returns to its nonconducting condition, said impedance means being of sufficiently large magnitude to limit flow of current to said coil to a safe value during sustained closure of said switch.

References Cited UNITED STATES PATENTS 2,801,374 7/1957 Svala 317-1485 X 3,018,419 1/1962 Bonn 317--148.5

3,210,614 10/1965 Welk 317--148.5 X

MILTON O. HIRSHFIELD, Primary Examiner.

J. A. SILVERMAN, Assistant Examiner. 

1. IN A SOLENOID CONTROL IN WHICH A COIL WOUND ON A CORE PRODUCES A MAGNETIC FLUX TO ATTRACT AN ARMATURE WHEN A SWITCH IS CLOSED TO CONNECT THE COIL IN A SERIES CIRCUIT WITH A VOLTAGE SOURCE AND A RESISTOR, THE IMPROVEMENT WHICH RESIDES IN CONNECTING THE OUTPUT TERMINALS OF A SWITCHING TRANSISTOR ACROSS SAID RESISTOR AND CONTROLLING THE ON-OFF CONDITION OF SAID TRANSISTOR IN ACCORDANCE WITH CHANGES IN MAGNETIC CONDITIONS IN SAID CORE, SAID RESISTOR BEING OF SUFFICIENTLY LARGE MANGITUDE TO LIMIT FLOW OF CURRENT TO SAID COIL TO SAFE VALUE DURING SUSTAINED CLOSURE TO SAID SWITCH. 